Providing fuses in integrated circuits is a practice well-known to those skilled in the art, especially in the manufacture of MOS circuits. For example, it is standard practice to provide fuses to protect MOS transistor gates against the accumulation of electrostatic charges which appear during the manufacture of integrated circuits. These fuses are then disrupted or fused to release the gates of the transistors. As another example, providing redundant word lines or bit lines in large capacity memories also relies on the use of fuses. The defective or unnecessarily redundant lines are then isolated from the rest of the memory by fusing or disrupting the fuses. In general, integrated circuit fuses are designed to be disrupted by the application of a fusing voltage or current to enable the modification of the configuration of a circuit at a final stage of manufacture.
A prior art fuse made by etching is of the type shown in FIG. 1. A fuse 1 of this kind, with a very simple structure and a small space requirement, includes a small bar-shaped central region 2 that widens out at its ends to form two zones 3, 4 receiving a plurality of electrical contacts 5, 6. In general, as can be seen in FIG. 2 in a sectional view, the fuse 1 is buried in an integrated circuit 10 where it is sandwiched between a lower layer 11 and an upper layer 12 of oxide deposited on a silicon substrate 13. The contacts 5, 6 take the form of metallized holes going through the oxide layer 12 to connect the zones 3, 4 to conductors 14, 15. Conventionally, the whole unit is made by the successive deposition of various layers of oxide, metal and/or polysilicon and by the etching of the layers by photolithography.
In order that the current density in the fuse 1 and the efficiency of the fusing may be a maximum for a given fusing current, the width W of the central region 2 of the fuse is usually chosen to be equal to the technological minimum width W.sub.min permitted by the manufacturing technology of the integrated circuit 10. For example, at present, the technological minimum width W.sub.min of the MOS type integrated circuits is commonly about 0.25 micrometers with respect to the minimum width of a conductor, i.e., the minimum length of the gates of the MOS transistors.
However, this precaution provides only a relative advantage, given that the technological minimum also determines the size of the other components present in the integrated circuit 10. This is particularly true with transistors, and their capacity to withstand high voltages or currents. Thus, in recent years, the reduction of the technological minimum width through the improvement of technologies has gone hand in hand with a reduction of the permissible fusing voltages and currents. For example, the maximum fusing voltages permitted in medium-scale integrated MOS circuits according to older technology were in the range of 5.5 to 6 volts. For large-scale integrated circuits formed using current technology, the maximum fusing voltages are no more than 1.8 to 2 volts.
Despite providing for a minimum width, a standard fuse does not, in statistical terms, provide a fusing efficiency equal to 100% under standard fusing conditions. In other words, when it is sought to simultaneously fuse or disrupt a set of fuses present in an integrated circuit by applying one or more fusing pulses of current or voltage, it frequently happens that non-disrupted fuses remain. These fuses have an electrical resistance which, although it is higher than their initial electrical resistance, cannot be compared to that of an open circuit. This drawback is reflected in the efficiency of manufacture of the integrated circuits, and becomes more of problem when several tens or even several hundreds of fuses are to be made in the same integrated circuit.
The technological minimum width W.sub.min therefore, represents an obstacle in the search for a fuse having high fusing efficiency. It is well known in the field of photolithography that the technological minimum width W.sub.min is determined by various technological constraints. In particular, obtaining satisfactory reliability of the gates of the MOS transistors is determined by the technological minimum width W.sub.min. Furthermore, a phenomenon of diffraction and reflection of light during the isolation of the organic resin etching masks exists, and is known to those skilled in the art as the "proximity optical effect".
Finally, another drawback of standard integrated circuit fuses is that they are not entirely reliable. A certain percentage of disrupted fuses have a tendency to regenerate for reasons as yet poorly explained. The regeneration of a fuse is expressed by the fact that its electrical insulation properties deteriorate, whereas they were initially satisfactory.